The present invention relates broadly to a data buffer apparatus, and in particular to a fully asynchronous input/output data buffer apparatus.
In the prior art, in any segment of a digital system in which the input and output of information are not synchronous, it is necessary that some provision be made for temporary data storage. While the long term average data rates must be substantially equal through any interface, the short term data rate differences must be handled. For systems in which the input and output rates vary, control of the data storage memory device becomes complicated. A system, for example, in which data is collected from several different sensors and stored on magnetic tape may involve not only nonuniform input data rates, but also an output data format which is not directly compatible with other system requirements.
One conventional solution to the problem is to use First-In-First-Out (FIFO) memory buffers. In a first-in, first-out buffer, the data at the input propagates serially toward the output in a manner not dependent on either the input or output clocks. Even if the input and output rates differ, data will be continuously available at the output. The only requirement is that the input and output rates never differ by so much that the buffer runs completely full or completely empty. Several problems are associated with a typical first-in first-out type buffer. If the required memory becomes large, substantial propagation delays occur between the input and the output. Moreover, these delays are not uniform, but depend on the amount of data stored in the memory. An additional problem is that the first-in, first-out memory is not a common logic element, and its limited availability can severely reduce the choice of logic configurations. Furthermore, the other system requirements such as availability of components from multiple sources, environment, operating speed, etc., may preclude its use entirely. The present apparatus avoids the problems associated with the first-in, first-out memory buffer by using random access memory (RAM) devices for data storage.